Various small electronic devices, commonly referred to as “dies,” are employed in radio frequency (RF) wireless communication devices. Conventionally, such electronic devices are attached to substrates (such as metal lead frames, laminate circuit boards, ceramic based board, or silicon based boards, for example), encapsulated, and covered with external shields (often referred to as “cans”) to form discrete shielded packages, which may be referred to as “modules.” The various types of electronic devices included in such shielded packages may include bulk acoustic wave (BAW) resonators, such as thin film bulk acoustic resonators (FBARs) and surface mounted resonators (SMRs), and/or surface acoustic wave (SAW) resonators, amplifier, transistors, transducers, and the like. The acoustic resonators may form RF transmit and receive filters, for example, corresponding to various transmit and receive frequency bands utilized by the wireless communication devices.
A conventional shielded package includes an encapsulation (e.g., reinforced or non-reinforced molding resin or mold compound) that covers the substrate and the electronic devices (e.g., “die”) with the package. An external shield generally includes electrically grounded metal layers that surround or cover the top and sidewalls of the package (including the mold compound and the package substrate), and protects the electronic devices within the shielded package against externally generated electromagnetic radiation (“external electromagnetic radiation”), preventing electromagnetic interference (EMI). The bottom of the shielded package is typically not covered by external metal layers, although the package substrate, ground layer(s), external connecting pins protruding from the substrate, and/or various electronic devices, transmission lines and other circuitry within the substrate generally provide sufficient external shielding from external electromagnetic radiation from the bottom of the shielded package.
In addition to the external shields, a conventional package may include metal cans, wires, and/or wire mesh formed between and/or around the electronic devices (or dies) to create device EMI shielding from internally generated electromagnetic radiation (“internal electromagnetic radiation”). The internal shields thus prevent EMI from occurring between and among the electronic devices within the shielded package. Conventionally, the internal shields are applied after attachment of the electronic devices to the package substrate. Various types of internal shields include but are not limited to wirebond loops assembled between electronic devices or surrounding particular electronic devices, metal filled trenches formed in mold compound between electronic devices or surrounding particular electronic devices, and/or wirebonds, wire mesh or metal lid formed over particular electronic devices. Such internal shields are assembled at the package level, meaning that the internal shields are added after the package has been at least partially fabricated, as mentioned above. For example, wirebond loops may be formed on a surface of the circuit board before application of the mold compound, while trenches may be formed after application of the mold compound (e.g., by laser ablation through the mold compound). The external shield is then applied over the mold compound and the electronic compounds and internal shields contained therein (e.g., using chemical vapor deposition or spraying) to provide the shielded package.
Formation of internal shields requires additional space between the electronic devices in the shielded package to accommodate placement of the internal shields. This typically results in the shielded package (and possibly the wireless communications device in which it is contained) to be larger. For example, providing a row of wirebond loops between two electronic devices on a circuit board requires approximately an additional 90 to 120 μm of separation, while providing a metal filled or lined trench between two electronic devices requires approximately an additional 100 to 175 μm of separation. However, the trend in design of RF wireless communication devices, such as cellular phones, has been to add more transmit and receive bands for worldwide usage, without increasing (or even possibly reducing) the size of the communication devices. Further demand is directed to increasing the number of bands and tightening filter performance requirements to allow cellular phones to receive and/or transmit through multiple bands, simultaneously. As these trends continue, RF isolation between transmit and receive filters in cellular phones becomes more critical. Accordingly, what is needed is shielding from both external and internal electromagnetic radiation that occupies less space in a shielded package and/or is easy to fabricate, while maintaining or improving EMI protection.